Wetback - Radiators - Gas Instant

Forums › Home Workshop DIY › Wetback - Radiators - Gas Instant - Heating System DIY

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149 posts

Master Geek

#1093770 22-Jul-2014 16:04

Each radiator will have the tap to change the flow, and they have the temperature control valve on them I believe which essentially opens and closes based on the temperature too, but no for cold water feed into each radiator...
Haven't heard about this at all... my parents install doesn't have this that's for sure.

However the output from the wetback wont be sufficient to require tempering anyway. I plan to be reading the temperatures and if they get too hot it will sound a warning and the fire can be turned down, however I doubt this would ever happen. If it really goes pear shaped and gets to near the limts of the pump, the pump would be shut off, the safety valve opened and the fire would just syphon heat the tank and it would bubble out the roof.

Thats my understanding of it thus far anyway...

Stan

929 posts

Ultimate Geek
Inactive user

#1093846 22-Jul-2014 18:39

This is what I was thinking of:

Its simple yet effective no heat exchangers needed.

With the wetback would just buy one from trade me as they seem to go for a reasonable price:
http://www42.trademe.co.nz/building-renovation/heating-cooling/heating-systems/auction-750710067.htm

If you do pick up a metro wetback make sure you fire cement it to the back of the fireplace well or it could melt.

WanaGo

149 posts

Master Geek

#1093860 22-Jul-2014 19:27

Hi Stan

Thanks for the image.

Yep thats the simple version, thermo syphon heat the tank, and pump the water to the radiators. 2 systems, yet share common water.

The problem is for me is the distance from the fire to the tank, and also I would prefer to pump around the wetback rather than syphon. Planning to have a decent sized wetback tubing inside.

Here is the latest diagram.

So this pumps around the radiators and the Wetback still, but its open air vented so the cylinder itself is under no or little pressure. Vent is purely there for safety, and will not have a head of water as such. Fill the tank to the required level and see the level from the sight glass on the side, which would be lower than the top of the tank.
Thought about an Ajax option, however that wont work as the system would experience pressure in the pipes when the pump is on, but no pressure when the pump is off, and the ajax wouldn't cope I don't think and would just fill the tank up and piss the water out the roof.

Idea 3

I changed the inlet and outlet around on the tank, so the water coming in from the fire will not have the resistance of pushing into water in the tank, it will just drop on the top, and the water level would be below the pipe inlet. If it had to push into water, it might be more inclined to pump out the vent instead. This way it wont.
The pump then pulls water out of the bottom of the tank and pumps it around.
The tank is not like a typical hot water cylinder since the water is pumped, it will be all stirred up and a fairly even temperature, so really can be thought more of an open (but insulated) bucket if anything. The top wont be hot and the bottom cold like a normal cylinder, so it wont matter if its pulling from the top or the bottom. Tank is also not under pressure really, so even if the pump is pushing a few bar, the tank wont see much of that at all.

While I do appreciate the simple system, I am still inclined to think this should work well if not better...
Only need the standard 2 port cylinder, rather than a 4 port, and also no heat exchanger is needed as they share the same water.

Comments welcome.

WanaGo

149 posts

Master Geek

#1093942 22-Jul-2014 21:37

Interesting document about wetback design if anyone cares

http://www.pulseflow.co.nz/Wetback%20Water%20Heating.pdf

wellygary

7377 posts

Uber Geek

#1093955 22-Jul-2014 22:16

Where dioes cold water enter the system?
As the tank is not sealed your losses through evap will be higher, so you will need and ability to top up your system fairly regularly,

also with a system like that you will never use the roof spout unless you are running the system almost dry and cresting steam pockets to push water up the spout,

WanaGo

149 posts

Master Geek

#1093968 22-Jul-2014 23:24

Havent pictured the cold water into the system.

Tank is sealed in the sense it has a lid on it etc, the only way out is via the vent tube, so the loss shouldn't be too much I wouldn't think.
The idea was to just have a manual tap on the system and periodically fill the system to a specified level. Start off with that anyway.

Correct about the roof spout, it wont be used for the normal purpose like head, it is just a way out of anything was to go wrong, if the system somehow was overfilled, overboiled (unlikely) etc etc.

The pump I am planning to use arrived this afternoon. had been sitting in the mail box all day, courier didnt bring it to the door. You can easily blow from inlet to outlet, so there is actually no need for a solenoid valve in the system at all. If the pump fails, then the fire could thermo syphon via the pump no problem. Longer trip via the radiators though. something to think about though.

The pump comes with a flow switch, and is used to detect if someone turns on a tap in the system, the pump can start automatically. So that shows that flow must be able to occur through the pump so the flow swtich can detect it and start the pump. Wont be using that feature, will have it in manual, and controlled to pump as required.

Really quite happy with the pump actually. This is the one I got: http://www.trademe.co.nz/Browse/Listing.aspx?id=754064024

On fast speed it can do 27L/min assuming no head, down to about 15L/min on slowest speed. Assuming the system is resistant to cut down at least half of that speed, that means I get say 7 to 13L/min. Will see what happens when its all together anyway.

Regards
WanaGo

Sidestep

1003 posts

Uber Geek

Lifetime subscriber

#1093992 23-Jul-2014 03:30

Stan's design is pretty much what we have.
The woodstove's freestanding in the corner, feed from hwc's under the floor, through the wetback, follows the flue into the ceiling space.
It's more than 5m from the tank, thermosyphons just fine.
Our routine's bank & choke the fire at bedtime, flip it open when we get up. Bank and choke it when we leave for work/school, kids chuck wood on & open it up when they get home.
Without the buffer of a tankfull of hot water our wall heaters would shut off in the early hours - when we need them most. In the evening when we have the fire really burning water's boiling in the wetback, almost boiling temp in the tank. With the draw of the heaters exceeding the heat provided by the banked fire, by morning the tank temps just right for showering.
We followed the temp in the loop a few nights when we were setting it up.
The wetback's actually a wetside. Loops of copper pipe along the long side of a rectangular firebox.
Works better than a wetback. After we bank the fire in the evening, the unburnt wood shades the pipe from heat for several hours until the wood in the firebox burns down enough that the loops are exposed to direct heat again. Even then with the fire choked down it only provides maintenance heat to the system until we open it up to burn again in the morning.

wellygary

7377 posts

Uber Geek

#1094026 23-Jul-2014 09:21

If the pump fails, then the fire could thermo syphon via the pump no problem. Longer trip via the radiators though. something to think about though.

But given that each of the Radiators has a the possibility of being turned off/down (via the thermo valves on the radiator panels ) in each of the rooms, then your flow rate back to the stove may not be enough to keep the wetback from boiling,

You really need to make sure there is a failsafe method of keeping the wetback cool.

WanaGo

149 posts

Master Geek

#1094047 23-Jul-2014 09:56

Hi Sidestep.

Thanks for the info. Yeah we are looking at putting in 2 sidebacks now, rather than 1 wetback, because of the size of our firebox. going to remove the fire bricks from the size and replace it with 2 skinny sidebacks, joined at the back of the fire and up the flue to the tank. The return in the latest design is coming from the raidators, so that will come from under the floor back into the fire, so just 1 pipe to go up into the ceiling at the fire place.

Hi Wellygary

Yep, all valid points. Radiators wont be turned off, but just because I say that doesnt mean its impossible to happen at one point in time. fair point. Maybe that return with the N/O valve is still worth having as a failsafe.

Thanks

andrewNZ

2487 posts

Uber Geek
Inactive user

#1094062 23-Jul-2014 10:18

So from what I see, it appears you don't plan to use a hot water cylinder as your "tank". That in itself looks like an oversight. If you use a standard HWC then you can use an ajax valve with no problems. You have no potential overflow in the house (no worries about blocked overflow drain pipes) because vent doubles as the overflow and safety in the event of a boil or failed ajax valve.

You'd be surprised how effective a thermosyphon is. You'd also be surprised how restrictive a solenoid valve is. In fact I'd be surprised if it allowed any flow at all, because there is no water pressure to force it open.
You're already saying you don't think a thermosyphon will work and then you're adding one as a "safety feature".

Honestly, I could never recommend complicating a system as you plan to. You're gaining nothing other than the cool factor of controlling it with something you wrote, and adding so many points of failure and potential safety risks it's not funny.

Stan's drawing is exactly what you need. You could still use smarts to control room temps if you want to.

KShips

153 posts

Master Geek

#1094101 23-Jul-2014 10:53

WanaGo:
KShips: Over the weekend we talked to a company at the Home Show about a gas radiator system (and whole house was somewhere around 8k estimate, can't dump that cash on system unfortunately), great looking system. $2k I think was the 28kw boiler and they have many customers who do radiators over a number of years to cut costs.

Back to DIY, I had been wondering if viable to build a second circuit to separate radiators for a wetback circuit (the pressure issues have always been of concern but proper design I presume would be fine). The Gas system if installed would kick in if the wetback system wasn't maintaining a decent temp (especially early morning when the fire is out). I like your idea about using valves and maybe have it on same system to switch between the 2 systems as needed. When reading the brochure the gas boiler does mention solar input so I wonder if can be used with wetback as well.

Thanks for this.
What was the company you talked to about the boiler, and $2K for 28Kw? Would be interested to talk to them.
Boiler assisting the wetback could be very helpful indeed.

I'm not 100% sure on that price/kw. I thought they had said 18kw but when I got home I realised the smallest was 24kw. It was 'Better Heatin Solutions' who are part of HydroFlow. They said to send in house plans and they will size and price according to house specs. I was very impressed with how up front they seemed to be, no 'Must buy today specials', gave overview of system, prices etc as ballpark idea until look at plans.

If using a Non pressured system such as what Stan has mentioned, what are the requirements (legal or insurance) around building it? (I'm hoping none

)

WanaGo

149 posts

Master Geek

#1094134 23-Jul-2014 11:43

andrewNZ: So from what I see, it appears you don't plan to use a hot water cylinder as your "tank". That in itself looks like an oversight. If you use a standard HWC then you can use an ajax valve with no problems. You have no potential overflow in the house (no worries about blocked overflow drain pipes) because vent doubles as the overflow and safety in the event of a boil or failed ajax valve.

You'd be surprised how effective a thermosyphon is. You'd also be surprised how restrictive a solenoid valve is. In fact I'd be surprised if it allowed any flow at all, because there is no water pressure to force it open.
You're already saying you don't think a thermosyphon will work and then you're adding one as a "safety feature".

Honestly, I could never recommend complicating a system as you plan to. You're gaining nothing other than the cool factor of controlling it with something you wrote, and adding so many points of failure and potential safety risks it's not funny.

Stan's drawing is exactly what you need. You could still use smarts to control room temps if you want to.

Why do you say I am not using the hot water cylinder as a tank?
It is the tank. Its just not under pressure, its just a holding vessel. This system is just for the radiators, it is not for our hot water system. I dont follow what you said at all about not using it as a tank.
If we use a standard HWC and an ajax value setup, that would assuming we are taking water out of the system, such as using it for a shower etc, which isnt the case. This is simply moving water around the system to provide heat to the radiators only. I dont see anywhere for potential overflow into the house with what I am proposing.

The solenoid valve I have found has a butterfly in it which turns 90 degrees. it is not restrictive at all.
I didn't think thermosyphon would work due to the distance to the tank, in terms of being efficient. In terms of being a safety so the water in the pipe doesnt boil - then yes that should work fine...

Looking at what I put, there is nothing complicated about it. Remove all the sensors and the only difference between what I am proposing and what Stan proposed, is instead of the fire auto syphoning to the tank and needing the tank to have 4 piped connections to it, I have the 2 piped connections using a standard water cylinder, and water being pumped through the wetback. That is the only difference. Whether the water from the radiator goes to the tank, or to the wetback.

There is no 'cool factor' about this. I am not going to risk the safety of our house or family just to get some kick out of being cool... that is not the reason at all. I think this system should work better based on what I have read, and who I have talked to. that is it, period. The only point of failure which is up for debate is the safety feedback through the solenoid valve. The system is pumped and in the rare case the pump fails and the path through the solenoid valve will on be there for safety only, so the wetback doesnt boil. Our fire will run maybe 1h going nicely without attention, and then dies down. Its not like we crank this up and leave it all day unattended. If the pump fails I will have some sort of alarm to notice it has happened. The fire can be damped down or put out, or if we are out then the safety will allow the system not to self distruct. The safety is not used at all other than if the pump were to fail.

Where are all these points of failure you are talking about, and safety risks.

The monitoring system is there only to monitor water temp so I can see the system is working and know what the water temp is at various points.

WanaGo

149 posts

Master Geek

#1094149 23-Jul-2014 12:02

Solenoid value is also not forced open by anything, its electrically operated with spring return, making it normally open when not powered, and closed when powered. So if power goes off then the safety path is open. If the flow switch on the pump detects no flow, then it will de-energise the valve and it will open.

andrewNZ

2487 posts

Uber Geek
Inactive user

#1094181 23-Jul-2014 13:19

I've clearly misunderstood some key factors. Much of what I've said is based on your drawing.

The type of solenoid you've found changes my opinion of that portion. I've never seen or heard of one like it, I'm glad you have.

I have my opinions, but hey, it's your project and I'm genuinely looking forward to knowing the results.

WanaGo

149 posts

Master Geek

#1094188 23-Jul-2014 13:35

OK fair enough.

Ill redo the drawing so its more accurate, and place it in a house so it shows the levels of things better too.

Also, since the pump is pumping out and also pushing back in on the return, the tank will be under neutral pressure, as Out = In. So really the tank can be thought of as an open bucket, there is no pressure involved. The pipe after the pump will be presurised, however when it gets back to the tank since the pump is drawing from the tank, the pressure is neutral.
The vent is just an escape path really, so this is an open vented system rather than being closed off and having an expansion chamber - as those are not allowed for wetbacks since its an uncontrolled source of heat. So really its an overflow more than anything since there is no pressure.
There is no mains or Ajax so there is no introduced pressure from that either. It will be manually filled to a level based on the sight glass, up to a predefined level, which may be part way up the vent pipe, so the tank is full. Unsure yet till we get closer to that stage.

So really it can just be thought of as a water trough that has a pump going out, and the same volume of water is coming back. The only way water will need to be introduced into the system is if there is a leak, or if there is evaporation or flow out of the vent tube.

Ill do another drawing which I hope will make things more clear.

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